This invention relates to a power unit supporting structure for supporting a power unit which has a engine proper, a clutch, a transmission and a differential gear, the clutch, the transmission and the differential gear being integrally connected with the engine proper.
In general, there has been known a front-engine and front-drive type vehicle or a rear-engine and rear-drive type vehicle in which an engine proper is disposed transversely of the vehicle body or in the right-and-left direction thereof so as to reduce the dimension of an engine room in the fore-and-aft direction for enlargement of the space inside a passenger room. In such a vehicle, as shown in FIG. 1, a transmission 3 is integrally connected with a transversely disposed engine 1 through the intermediary of a clutch 2, and a differential gear 4 is in turn integrally connected with the transmission 3 so that the clutch 2, the transmission 3 and the differential gear 4 jointly constitute a so-called trans-axle 5 which in turn forms, together with the engine proper 1, a power unit 6. Arrow F indicates the forward direction of the vehicle. The power unit 6 is supported by a vehicle body 8 through a plurality of supporting means 7 each having an insulator 7a molded from rubber so that vibrations of the power unit 6 to be transmitted to the vehicle body 8 can be reduced to a substantial extent by means of the rubber insulators 7a. Connected with the differential gear 4 through joints 11, 12 are a pair of drive shafts 9, 10 extending laterally from the right and the left side thereof, the right-hand side drive shaft 9 on the side of the engine proper 1 being longer than the left-hand side drive shaft 10 on the side of the transmission 3 due to the fact that the engine proper 1 is disposed offset to the left from the center of the vehicle body. Therefore, the right-hand side drive shaft 9 is comprised of an intermediate shaft 9a arranged in concentric relation with the rotation axis C of the differential gear 4, and an end shaft 9b coupled as its one end with the intermediate shaft 9a through an intermediate joint 13 and at its other end with a wheel 14b. The end shaft 9b is designed to be of the same length as that of the left-hand side drive shaft 10 so that the shafts 10 and 9a are disposed at the same angle of inclination with respect to rotation axis C of the differential gear 4 thereby to the prevent generation of an unequalized steering torque. The intermediate shaft 9a is coupled at its one end with the output shaft or rotation axis C of the differential gear 4 through the joint 11 and supported at its other end by the power unit 6 through an intermediate bearing 15 attached thereto so as to be retained in alignment with the rotation axis C of the differential gear 4. Thus, when the right-side and the left-side wheels 14b and 14a are caused to bounce or rebound during travel of the vehicle, the intermediate joint 13 and the transmission-side joint 12 are flexed to absorb the oscillatory motions of the wheels 14b, 14a.
In this connection, it is to be noted that although the power unit 6 is itself supported on the vehicle body 8 by virtue of the plurality of supporting means 7, as illustrated in FIG. 1, the power unit 6 is forced due to the oscillatory motions of the wheels 14b, 14a to displace in a rolling manner thereby to deformably oscillate the rubber insulators 7a of the supporting means 7 around a central axis of rolling P, which extends through the differential gear 4 at an angle to the rotation axis C thereof. In other words, the power unit 6 is caused to oscillate greatly during abrupt changes of torque, thus developing rolling displacements.
With such a conventional support structure for the power unit 6, the axis of rolling P of the power unit 6 extends obliquely and intersects the rotation axis C of the differential gear 4 at an angle thereto so that, when the power unit 6 is caused to rollingly displace, the respective joints 11, 12 and 13, particularly the joints 12 adjacent the transmission 3 and the joint 13, are moved in a vertical direction. At this time, if the wheels 14b, 14a are bounced or rebound greatly in a direction to increase the flexing rate of the joints 12, 13, these joints 12, 13 will likely be flexed excessively beyond the allowable range of flexure. As a result, the transmission efficiency of driving force is lowered, and if the allowable range of flexure is exceeded upon bouncing of the wheels 14b, 14a, the ground-engaging forces of these wheels are reduced to impair the steering function, thus resulting in a very dangerous situation. In order to avoid such a situation, it is considered to decrease necessary the bouncing or rebounding stroke of the wheels and/or to stiffen the support means 7, but these measures give rise to another problem in that riding comfort of the vehicle is worsened.